I have this part for my S2000 - it's a nice piece of kit from Laile, the hardware included is nice, too. My instructions were in Japanese but pretty self-explanatory with the blown-out graphics and some common sense. Unless your car is a mm off the ground and doing 140 mph into turn 13 at Indy there will be no discernible difference in drag
I can't say with 100% certainty but it feels like the S2000 warms up quicker and runs a little hotter with the plate over the plastic. Maybe a thermal conductivity expert can chime in on the difference between a thin aluminum and thin plastic polymer sheets. No overheating issues, could also be my imagination.
It is a little bit of a pain to get on/off due to its size and very tight mounting tolerance. When I put mine on initially I was happy to have a buddy hold half up to line everything up because there is virtually no slop/play. Something to consider if you need to access your underside regularly, although I'm sure you can concoct some sort of quick fastener locks on a couple of the mounting holes to help you out.
Lastly, consider the sheer ability of plastic over aluminum - just like in a crash, you want things to give way/crumple/break before hurting the vital parts. This is akin to a motorcycle debate on (poor) frame sliders/skid plates doing more damage than good if the mounting is ill-thought. What if you run over a big rock on the road? This ain't no Tesla titanium plate.
Edit: pic for proof
